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CHROME STEELS                                    185

incinerated in an efficient draught-chamber to expel the mercury. The
residue is strongly ignited, allowed to cool, mixed in the crucible with 8-10
parts of a mixture of 4 parts of sodium carbonate with I part of potassium
bitartrate, and heated carefully so as not to burn the carbonaceous residue
entirely away.

The chromium then remains as oxide, whilst the vanadium, molybdenum
and tungsten form the sodium salts of the respective acids. The crucible
is next heated with water in a beaker, the crucible extracted and the in-
soluble residue of chromic oxide and carbon filtered off, washed first with
water containing a little sodium carbonate and then with water acidified
with nitric acid, dried and ignited in a tared platinum crucible. The chromic
oxide thus obtained may be weighed directly. The result may be con-
trolled volumetricalry by heating the oxide with a mixture of sodium car-
bonate and magnesium oxide (see Ferro-silicon), dissolving the resultant
mass in hydrochloric acid, making up to volume in a 500 c.c. measuring
flask and titrating the chromium in an aliquot part (see i,a}.

2.  Determination of the Carbon, Silicon, Phosphorus, Sulphur
and Arsenic.—The methods used for ordinary steels are applicable (see
Iron, i, 2, 4, 5 and 6).

3.  Determination of the Manganese.—The residue remaining undis-
solved on lixiviation of the fused mass (see I, a) is dissolved in hydrochloric
acid and the manganese determined in this solution, which contains also
all the iron (see Ferro-silicon, 3).

*
* *

Chrome steels may contain 0-3-4% °f chromium (usually 1-2%), 0-3-1-6%
of carbon, 0-05-0-3% of silicon, 0-5-1% of manganese, and traces of phosphorus
and sulphur (0-01-0-04%). Extra hard steels contain 2-3% of chromium and
1-5-1-6% of carbon. Nickel, vanadium, tungsten, silicon, etc., are often asso-
ciated with the chromium (chrome-nickel, chrome-vanadium, chrome-tungsten,
chrome-silicon, etc., steels).

It should be noted that small proportions of chromium (less than 0-1%) are
found in almost all ordinary steels.

The following table gives the percentage compositions of some commercial
samples of chrome steels (Geiger) :

TABLE IX
Composition of Chrome Steels

No.
	C
	Si
	Mn
	P
	S
	Cr

I        ...
	0-311
	0-149
	0-98
	0-039
	0-031
	0-361

2
	0-382
	0-279
	1-03
	0-035
	0-042
	1-045

3       •     •     •
	0-895
	0-280
	0-97
	0-018
	0-014
	0-480

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